bashreturnarray

#!/bin/bash

# Set a global array value to test variable lifetimes.
myarr=( sample global array )

## The next set of functions are called, directly or indirectly,
## by the primary functions

return_array_building_string()
{
    local ESEP="$1"

    # Change IFS to break ONLY at newlines to prevent
    # breaks between words of multi-word array elements:
    local IFS=$'\n'

    local -a arr=(
        "one"
        "two words"
        "three
lines of
words"
    )

    # echo "View array before sending back to caller:"
    # printf "'%s'\n" "${arr[@]}"

    # The magic occurs in the next two lines.  Using the '*' instead 
    # of the '@' instructs BASH to use the first character of the IFS
    # (which we also change below) between the elements.
    IFS="${ESEP}"
    echo "${arr[*]}"
}

generic_array_string_builder()
{
    local IFS="$1"
    echo "${*:2}"
}

return_array_building_string_with_generic_function()
{
    local IFS="$1"
    local -a arr=(
        "one"
        "two words"
        "three
lines of
words"
    )

    generic_array_string_builder "${IFS}" "${arr[@]}"
}

reset_myarr()
{
   myarr=( $( date +"%Y %m %d" ) )
}

demo_reset_by_name()
{
   local -a myarr
   reset_myarr

   echo "In demo_reset_by_name(), after calling reset_myarr(), the elements of myarr are:"
   printf "'%s'\n" "${myarr[@]}"
   echo
}

reset_by_read()
{
    target="$1"
    arr=( $( date +"%Y %m %d" ) )

    read -a "${target}" < <( echo "${arr[@]}" )
}

demo_reset_by_read()
{
    local -a myarr
    reset_by_read "myarr"

    echo "In demo_reset_by_read(), after calling reset_by_read(), the elements of myarr are:"
    printf "'%s'\n" "${myarr[@]}"
    echo
}

reset_by_mapfile()
{
    target="$1"
    arr=( $( date +"%Y %m %d" ) )

    # This construction does not work, result is no elements
    # echo "${arr[@]}" | mapfile -t "${target}"

    # This construction does not work, result is single element with spaces
    # mapfile -t "${target}" < <( echo "${arr[@]}" )
    
    # This is the proper construction.
    local IFS=$'\n'
    mapfile -t "${target}" < <( echo "${arr[*]}" )
}

demo_reset_by_mapfile()
{
    local -a myarr
    reset_by_mapfile "myarr"

    echo "In demo_reset_by_mapfile(), after calling reset_by_mapfile(), the elements of myarr:"
    printf "'%s'\n" "${myarr[@]}"
    echo
}


## Following functions are the primary functions, called with a case
## statement sorting the input parameters on the command line:

simple_return_array_string()
{
    local ESEP=$'\a'

    # Uncomment the following to see what the returned string looks like:
    # local arrstr=$( return_array_building_string "${ESEP}" )
    # echo "arrstr = '${arrstr}'"

    local IFS="${ESEP}"
    local -a locarr=( $( return_array_building_string "${ESEP}" ) )
    printf "'%s'\n\n" "${locarr[@]}"
}

generic_return_array_string()
{
    local ESEP=$'\a'
    local IFS="${ESEP}"
    local -a locarr=( $( return_array_building_string_with_generic_function "${ESEP}" ) )
    printf "'%s'\n\n" "${locarr[@]}"
}

fake_return_reset_by_name()
{
    echo "In fake_return_reset_by_name(), the elements of myarr are:"
    printf "'%s'\n" "${myarr[@]}"
    echo

    demo_reset_by_name

    echo "Back in fake_return_reset_by_name(), the elements of myarr are:"
    printf "'%s'\n" "${myarr[@]}"
    echo
}

fake_return_reset_using_read()
{
    echo "In fake_return_reset_using_read(), the elements of myarr are:"
    printf "'%s'\n" "${myarr[@]}"
    echo

    demo_reset_by_read "myarr"

    echo "Back in fake_return_reset_using_read(), the elements of myarr are:"
    printf "'%s'\n" "${myarr[@]}"
    echo
}

fake_return_reset_using_mapfile()
{
    echo "In fake_return_reset_using_mapfile(), the elements of myarr:"
    printf "'%s'\n" "${myarr[@]}"
    echo

    demo_reset_by_mapfile "myarr"

    echo "Back in fake_return_reset_using_mapfile(), the elements of myarr:"
    printf "'%s'\n" "${myarr[@]}"
    echo
}

# echo "Original contents of global variable myarr:"
# printf "%s\n" "${myarr[@]}"
# echo

# demo_returning_array_strings
# demo_constructing_arrays_at_known_names

# echo
# echo "Confirm the global-scope array was not touched:"
# printf "%s\n" "${myarr[@]}"


prognum="$1"

case $prognum in
    1) echo "simple_return_array_string()"
         simple_return_array_string
         ;;
    2) echo "generic_return_array_string()"
         generic_return_array_string
         ;;
    3) echo "fake_return_reset_by_name()"
       fake_return_reset_by_name
       ;;
    4) echo "fake_return_reset_using_read()"
       fake_return_reset_using_read
       ;;
    5) echo "fake_return_reset_using_mapfile()"
       fake_return_reset_using_mapfile
       ;;
esac